init
        |
        V
      HELLO
    /   |   \
   /    |    \
  /     |     \
GET    UNL    PUT
 |      |      |
 V      V      V
DATA-->EXIT<--DATA
        |
        V
       end

##</code><code>##

+---+  cmd  +---+     +---+
| B |------>| W |---->| S |
+---+       +---+     +---+
              |
              |       +---+
               ------>| F |
                      +---+

##</code><code>##

+---+  DATA  +---+
| B |------->| W |
+---+        +---+
              | |
  ------------   -----
 |                    |   +---+
 |              --------->| S |
 |             |      |   +---+
 V             |      |
+---+  data  +---+     -->+---+
|   |------->| W |        | F |
+---+        +---+------->+---+